This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
The mental effects of fasting have been known for ages and have been much discussed by all writers on fasting. A few years ago a group of young men and women at the University of Chicago lived for one week without food. During this period they attended their classes and engaged in their usual sports, following out their usual routine. Their mental alertness was so much greater during the period that their progress in their school work was cited as remarkable. Several repetitions of this experiment, always with the same results, proved that this was not exceptional.
All the purely mental powers of man improve while fasting. The ability to reason is increased. Memory is improved. Attention and association are quickened. The so-called spiritual forces of man--intuition, sympathy, love, etc.--are all increased. All of man's intellectual and emotional qualities are given new life. At no other time can the purely intellectual and aesthetic activities be so successfully pursued as during a fast.
Sinclair says: "I went out of doors and lay in the sun all day, reading; and the same for the third and fourth days--intense physical lassitude, but with great clearness of mind. After the fifth day I felt stronger, and walked a good deal, and I also began some writing. No phase of the experience surprised me more than the activity of my mind, I read and wrote more than I had dared to do for years before."
The old Roman proverb, "a full stomach does not like to think," well expresses a fact that is known to all mental workers. A full meal leaves them dull, unable to think clearly and continuously and often makes them stupid and sleepy. Mental workers have learned to eat a light breakfast and lunch and have their heavy meal in the evening after the day's work is done. When I was a high school boy, I used to miss a meal entirely when I knew I had an examination ahead. At that time I knew nothing of fasting, but I had learned that I could think better on an empty stomach. These facts are due to physiological causes. Large amounts of blood and nervous energies have to be sent to the digestive organs to digest a meal. If these energies are not required there, they may be drawn upon by the brain in thinking.
In my experience with fasting, I seldom see any increase in mental powers at the beginning of a fast. This is because we deal with the sick and these people are all inebriates and addicts--food inebriates, coffee and tea inebriates, tobacco and alcohol addicts. As soon as these things are taken from them they suffer a period of depression with headaches and various slight pains. After a few days, that is, when the body has had sufficient time to readjust itself and overcome the depression, the mind brightens up. The special senses also become acute.
Levanzin says: "But if physical strength is not lost during a fast, the mental power and clarity are extraordinarily increased. Memory develops itself in a wonderful way, imagination is at its best." One of the most remarkable things about the fast, one that impresses patients even more than the physical gains made while fasting, is the mental benefit that accrues from a period of abstinence. The clearness of the mind, the ease with which previously difficult problems can be handled, the improvement of memory, etc., all surprise and please the patients. These improvements must be attributed to the clearing of the brain of toxins.
The almost universal testimony of fasters is that their mind becomes clearer and their abilities to think and solve intricate problems are enhanced. They are more alert and their minds seem to open up into new fields. This increase in mental power may not manifest in the first few days of the fast, due to the fact that when patients are taken off their coffee, tea, alcohol, stimulating viands, etc., there is likely to be a general physical and mental let-down. But after a few days, re-action sets in and they improve both physically and mentally. Experiments on students have shown that short fasts greatly enhance mental powers.
Why should fasting result in an increase in mental abilities? Primarily, I think, because it affords the body an opportunity to throw off its load of toxins, hence the brain is fed by a cleaner blood-stream. Secondarily, I think that the rest of all the functions of life that fasting provides, supplies the brain with more power to think. Who can doubt that modern living tends to dull the mental powers? Especially our national drug addictions and our almost universal overeating tend to reduce mental abilities.